We, their hearts, become fearful just thinking of loved ones who go away forever, or of moments that could have been good but weren't, or of moments that could have been found but were forever hidden in the sands.
No one is alone during tribulations - there's always someone else thinking, rejoicing or suffering in the same way. This thought gives us strength to face the challenge that lies in front of us.
However happy people say they are, nobody is satisfied: we always have to be with the prettiest woman, buy a bigger house, change cars, desire what we do not have.